This invention relates to systems and methods for treatment of workpieces, such as semiconductor wafers, with an ion beam and, more particularly, to methods and apparatus for measuring the incidence angle and divergence of the ion beam.
In the manufacture of semiconductor devices using ion implantation, it is sometimes desirable to provide beam incidence angles which are other than perpendicular to the substrate plane. A description of ion implantation techniques using tilted implantation steps can be found in U.S. Pat. No. 5,696,382, issued Dec. 9, 1997 to Kwon, and U.S. Pat. No. 5,909,622, issued Jun. 1, 1999 to Kadosh et al. As device geometries are reduced, semiconductor manufacturers increasingly require improved accuracy in measuring and controlling beam incidence angle in ion implanters.
Further, semiconductor device manufacturers typically require the use of parallel scan techniques, wherein the ion beam has a constant angle of incidence on the semiconductor wafer.
Prior art techniques for measuring beam incidence angles typically involve measurement of the wafer chuck or supporting hardware at maintenance intervals. Such measurements can be correlated with implant angles determined by crystallographic examination of test wafers implanted at specified settings. Such techniques are tedious, have limited accuracies, do not provide real time measurements of the beam and do not provide any measurement of beam divergence.
U.S. Pat. No. 5,180,918, issued Jan. 19, 1993 to Isobe, describes a method and apparatus for measuring ion beam collimation, shaping the ion beam and controlling scanning thereof. The method utilizes a time-dependent change in the scanning position of the ion beam at an upstream location and a downstream location at mutually corresponding times.
It is desirable to provide a simple sensor system which allows ion beam incidence angle to be monitored in real time in order to comply with requirements of semiconductor manufacturers for reduced incidence angle tolerances. It is also desirable to determine deviation from a desired incidence angle, to permit accurate adjustment thereof, and to determine beam divergence (angular variation across the beam).
In one aspect, the invention relates to a sensing device which monitors the incidence angle of an ion beam in real time. The sensing device includes an aperture plate having an aperture for intercepting the ion beam and passing a beam portion therethrough, and a sensor located in the substrate plane or a plane parallel thereto behind the aperture and having a length along which the beam portion impinges on the sensor at a location which is a function of the incidence angle of the ion beam, the sensor being configured to produce a sensor signal indicative of the location of impingement of the beam portion on the sensor and representative of incidence angle. A computing unit may be configured to receive the sensor signal and compare it to a predetermined function for determining the incidence angle of the ion beam from the sensor signal.
The sensing device described above provides an incidence angle measurement with respect to one dimension of the substrate plane. Two dimensional measurement may be provided with an X-Y angle sensing apparatus which includes first and second sensing devices disposed orthogonal to each other in a plane parallel to the substrate plane.
The invention may be used while a semiconductor wafer is being processed, providing data on ion beam characteristics during implant. The sensing device may be mounted in an ion implanter to intercept unused areas of the ion beam to permit concurrent ion implantation and beam monitoring. Additionally, as beam properties are held stable, mechanical alignments may be checked for precision and accuracy, without the use of cumbersome measurement devices or procedures. Monitoring may be performed in vacuum, thereby eliminating possible discrepancies between measurements in vacuum and measurements in atmosphere.
According to another aspect of the invention, apparatus is provided for sensing an incidence angle of an ion beam on a substrate plane. The apparatus comprises an aperture plate having an aperture for passing a portion of the ion beam, and a position-sensitive sensor spaced from the aperture plate and located in or parallel to the substrate plane for intercepting the beam portion and producing a sensor signal that is representative of a location of impingement of the beam portion on the sensor and is thereby representative of the incidence angle of the ion beam on the substrate.
The position-sensitive sensor may comprise a resistor block having a length along which the beam portion impinges on the sensor and an output terminal which produces the sensor signal. The apparatus may further comprise a computing unit for determining the incidence angle of the ion beam in response to the sensor signal. The computing unit may determine the incidence angle of the ion beam from calibration data.
According to a further aspect of the invention, apparatus is provided for sensing divergence of an ion beam. The apparatus comprises a first incidence angle sensor for sensing a first incidence angle of the ion beam with respect to a substrate plane, a second incidence angle sensor, spaced apart from the first incidence angle sensor, for sensing a second incidence angle of the ion beam with respect to the substrate plane, and a computing device for determining divergence of the ion beam based on the first and second incidence angles.
The first and second incidence angle sensors may each comprise an aperture plate having an aperture for passing a portion of the ion beam, and a position-sensitive sensor spaced from the aperture plate and located in or parallel to the substrate plane for intercepting the beam portion and producing a sensor signal that is representative of a location of impingement of the beam portion on the sensor and is thereby representative of the incidence angle of the ion beam on the substrate plane.
The computing device may determine the first and second incidence angles based on calibration data and may determine divergence of the ion beam based on a difference between the first and second incidence angles.